BACKGROUND

[0001] Several types of large rotating machines have rotors mounted in a manner to be concentric to, and in a predetermined axial alignment with, a stator. While smaller rotating machines typically have a frame to which the stator is made integral and to which the rotor is mounted, locking the relative positions between the rotor and the stator, some larger rotating machines have stators and rotors independently supported to the ground. The relative position between the rotor and the stator is carefully adjusted at the time of assembly, with a view of achieving a perfectly annular air gap configuration, after which the machine can be put into operation. Many subsequent interventions can lead to highly undesired downtime, and therefore much care can be put into achieving a good fit at the time of assembly.

SUMMARY

[0002] It was found that notwithstanding such initial adjustments, the air gap configuration could evolve over time and concentricity or ovality defects, for instance, could appear due to a number of reasons, such as changes in temperature, magnetic flux imbalance caused by rotor shorted turns, wear of one or more bearings or other component, to name a few. Such defects in air gap configuration which appear during operation are typically undesired. They can lead to premature wear, for instance.

[0003] It was found useful, at least in some embodiments, to provide a rotary machine with an air gap configuration adjustment system having sensors providing a signal indicative of the air gap configuration during operation, and actuators configured to move a corresponding portion of the rotor or stator relative to the other one of the rotor and stator, to correct a defect in the air gap configuration which has appeared during operation. Indeed, a computer can be used to process signals received from sensors in a manner to monitor the air gap configuration and identify defects in the air gap configuration. Upon identifying a defect, the computer can determine a required correction, and the actuators can be controlled accordingly, in real time. A concentricity defect can be corrected by translating the axis of one of the rotor and stator relative to the axis of the other one of the rotor and stator, for instance, whereas an ovality defect can be corrected by stretching or compressing the stator across its diameter, for instance, to name two examples of possible corrections.

[0004] Accordingly, in accordance with one aspect, there is provided: a stator shape correction system for large rotating machines includes adjustable/automated stator anchoring system, an air gap monitoring system, a user interface and a management software that drives the automated anchoring. The automated anchoring is activated on demand by the airgap monitoring system through the management software based on the air gap monitoring system algorithm output. It is also said that a comprehensive magnetic flux monitoring system could be used: replacing the air gap sensors by magnetic flux sensors and using only one air gap sensor strategically positioned.

[0005] In accordance with another aspect, there is provided : a rotary machine having a rotor and a stator, a plurality of sensors configured to provide a signal indicative of an air gap configuration between the stator and the rotor, at least one of the rotor and the stator being supported via at least one actuator capable of moving a corresponding portion of the rotary machine relative to a ground reference, a computer configured to receive the signal from the plurality of sensors, determines a defect in the air gap configuration based on said signal, and controls the at least one actuator to correct the defect in the air gap configuration, during operation of the rotary machine, while the rotor rotates

[0006] In accordance with another aspect, there is provided : a computer-implemented method of monitoring and correcting air gap defects in a rotary machine having a rotor, a stator, and an air gap between the rotor and the stator, at least one of the rotor and the stator being supported via at least one actuator, the method being performed during rotation of the rotor relative to the stator, and comprising : using a plurality of sensors, generating a signal indicative of a configuration of the air gap; determining a defect in the air gap configuration based on said signal, and controlling the at least one actuator to correct the defect in the air gap configuration.

[0007] In accordance with another aspect, there is provided: a gearless sag mill having a rotor and a stator, a plurality of sensors configured to provide a signal indicative of an air gap configuration between the stator and the rotor, at least one of the rotor and the stator being supported via at least one actuator capable of moving a corresponding portion of the rotary machine relative to a ground reference in a manner to change the air gap configuration.

[0008] In accordance with still another aspect, there is provided a computer program product stored on a non-transitory memory media and comprising computer readable instructions to receive an input from a plurality of sensors, the input being signal indicative of a configuration of an air gap between a rotor and a stator of a rotary machine; determining a defect in the air gap configuration based on said signal, and controlling the at least one actuator to correct the defect in the air gap configuration.

[0009] It will be noted that although the embodiments presented below use a computer which can be wire connected to the sensors and to the actuators, it will be noted that in alternate embodiments, the computer can be wireless connected. Moreover, it will be understood that the processing of the sensor signal can be performed remotely, such as in the cloud, by exchanging data over the Internet, rather than by an on-site computer. As such, in some embodiments, it can be preferred to provide the air gap monitoring and correction system without local processing capabilities, but simply with means to transmit and receive data over the Internet.

[0010] It will be understood that the expression“computer” as used herein is not to be interpreted in a limiting manner. It is rather used in a broad sense to generally refer to the combination of some form of one or more processing units and some form of non-transitory memory system accessible by the processing unit(s). The use of the expression“computer” in its singular form as used herein includes within its scope the combination of a two or more computers working collaboratively to perform a given function. Moreover, the expression “computer” as used herein includes within its scope the use of partial capacities of a processing unit of an elaborate computing system also adapted to perform other functions. Similarly, the expression 'controller' as used herein is not to be interpreted in a limiting manner but rather in a general sense of a device, or of a system having more than one device, performing the function(s) of controlling one or more device such as an electronic device or an actuator for instance. [0011] It will be understood that the various functions of a computer or of a controller can be performed by hardware or by a combination of both hardware and software. For example, hardware can include logic gates included as part of a silicon chip of the processor. Software can be in the form of data such as computer-readable instructions stored in the memory system. With respect to a computer, a controller, a processing unit, or a processor chip, the expression “configured to” relates to the presence of hardware or a combination of hardware, firmware and software which is operable to perform the associated functions.

[0012] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.

DESCRIPTION OF THE FIGURES

[0013] In the figures,

[0014] Fig. 1 is a photograph of a sag mill;

[0015] Fig. 2 is a schematized cross-sectional view of a sag mill having an exaggerated ovality defect;

[0016] Fig. 3 is a polar graph showing stator shape vs. temperature derived from data obtained via an Air Gap Monitoring System (AGMS) having twelve (12) sensors;

[0017] Fig. 4 is a display of a user interface of the AGMS;

[0018] Fig. 5 is a flow chart illustrating a process of correcting an air gap defect in accordance with one embodiment;

[0019] Fig. 6A is a schematic of a rotary machine, having another embodiment of a monitoring and correction system having four sole plate actuators and four air gap sensors;

[0020] Fig. 6B is a block diagram of the monitoring and correction system of Fig. 6A;

[0021] Fig. 6C is a flow chart of a process of correcting an air gap defect which can be used with the system of Fig. 6A; [0022] Fig. 7 is a XY graph showing air gap distance values obtained both: from magnetic field intensity using Magnetic Field Monitoring System (MFMS) and air gap distance obtained from AGMS;

[0023] Fig. 8A is a schematic of a rotary machine, having another embodiment of a monitoring and correction system having four sole plate actuators and four magnetic flux sensors;

[0024] Fig. 8B is a block diagram of the monitoring and correction system of Fig. 8A; and

[0025] Fig. 8C is a flow chart of a process of correcting an air gap defect which can be used with the system of Fig. 8A.

DETAILED DESCRIPTION

[0026] Fig. 1 shows an example of a SAG mill 2, one type of large rotating machine.

[0027] Fig. 2 schematizes, in a somewhat exaggerated manner, an ovality defect 4 which was detected using an air gap monitoring system having a plurality of sensors circumferentially interspaced from one another. In the case of SAG and Ball mills, for instance, such a circularity defect can occur due to thermal expansion, but can even be present on a stopped machine which has reached ambient temperature. More specifically, the SAG mill 2 has a rotor 6 mounted in a manner to extend inside a stator 8. An air gap 10 extends in the form of an annular spacing between the rotor 6 and the stator 8.

[0028] Fig. 3 presents actual measurements of an air gap 10 of a SAG mill 2 as a function of angular position and temperature. As seen in the graph 12, the ovality increases with temperature, reaching its greatest extent at 61° C which was the highest temperature reached during this test. Such air gap configuration behaviour can stem, in the case of a SAG mill 2, from the fact that the stator 8 is supported on a few points: typically three and sometimes only two. In many cases, SAG mill 2 designers rely on the stiffness of the stator 8 core 14 and frame 16 to keep the uniform shape or constant diameter all around.

[0029] The air gap 10 is a significant design parameter for many large rotating machines. In situations where the rotor 6 is very large, it can be preferred to assess the rotor 6 shape before addressing stator 8 shape. The rotor 6 can suffer non uniformity usually referred to as roundness anomaly. The case of SAG and Ball mills involve salient pole rotor which make it more difficult to build keeping the same diameter for each pole attached to rotor frame. The difficulty comes also from the large size of such machines. Because of the big dimension, the machines cannot be transported in one piece on site via the roads so the machine’s final assembly is done on site, often with limited means. As for the poles, they are fixed, on site, around the rim. The rotor 6 roundness is one of the points to consider before controlling the stator 8 shape. The stator 8 shape can then be controlled by adjusting stator sole plates, for instance. For that reason, an example assembly protocol can begin with the confirmation of rotor 6 specifications using an air gap monitoring system.

[0030] In the case of a SAG mill 2 having a 10 m diameter, the nominal air gap 10 can be of 15mm +or-10% as specified. It was found that a machine that is well adjusted all around cold at standstill may show surprising results under its different operating conditions.

[0031] As will now be exemplified, the evolution of the stator 8 shape can be adjusted while in operation.

[0032] Figure 4, is an example of instantaneous results from an air gap monitoring system of a gearless SAG mill 2; it is showing indications to understand the stator 8 shape correction need on that type of machine with the following results:

[0033] · 0”04 mm @ 73 degrees for the rotor 6 center

[0034] · 0.70 mm @ 313 degrees for the stator 8

[0035] · 1.48 mm is the rotor 6 circularity

[0036] · 8.10 mm is the stator 8 circularity.

[0037] While the rotor 6 is well centered with an acceptable circularity, the stator 8 is also well centered but its circularity is bad at 8.10 mm.

[0038] Figure 4 shows actual results obtained from air gap monitoring system (AGMS) installed on a Gearless Sag Mill 2. That Gearless Sag Mill 2 is equipped with twelve (12) stator 8 mounted airgap sensors. The air gap monitoring system is the input for the stator shape control (SSC). Figure 4 shows representation of the rotor 18 inside the stator 20 and some calculated results 22 using the many algorithms that are part of the AGMS software and firmware. In this application, the rotor 6 shape is acceptable with 1.48 mm of circularity which is within the rotor’s specifications. However, the stator 8 is showing a much worse condition with 8.10 mm of circularity. As indicated in figure 4, the rotor 6 circularity is 9.27% while the stator 8 circularity is 60%. Figure 3 shows stator 8 graphic 12 shape illustration changes over temperature changes which are clear indication of the stator 8 shape defects. In this case, the oval shape is always present getting worst with temperature rise. A good way to visualize the situation is shown at figure 2. Using the same results as in figures 3 & 4, an image illustration is made to emphasize the machine stator problem to help visualize the situation. Figure 2, is also showing the major physical attachment points 22 holding the stator 8, these are the possible locations 22, 24 where the corrective actions 34, 36, 38, 40 can be applied using the SSC (stator shape control). In that case, the air gap 10 has twelve sensors equidistant around the stator 8 and only 2 locations 22, 24 are available for the actuators 26, 28, 30 32. The number of air gap sensors is twelve (12) while the number of actuators 26, 28, 30, 32 is four (4) in two (2) locations 22, 24; the two locations are called left 22 (L) and right 24 (R). The 2 actuators per location 22, 24 are horizontal and vertical. On the left side, the horizontal actuator 28 is LH and the vertical actuator 26 is LV and on right side, are horizontal actuator 30 is RH and vertical actuator 32 is RV.

[0039] The twelve (12) air gap sensors feeding the air gap monitoring system are providing the average minimum air gap (AMAG) of the whole machine. The AMAG value is then used as a target value to position the four (4) actuators 26, 28, 30, 32.

[0040] In that application, the process description, presented at Fig. 5, includes continuous monitoring of the rotor 6 shape which is possible since the commercialization of AGMS. For that reason, the flow chart 42 has a part dedicated to the rotor 6 shape. Even if the rotor 6 is monitored in real time, the real time correction concerned the stator 8 only.

[0041] Fig. 5 illustrates one embodiment for a rotor 6 equipped with salient poles. Where i = R (Right) & L (Left), S = number of stator 8 fixed sensors, N = number of poles on the rotor 6 of a salient pole machine, the flow chart 42 being air gap based for salient pole machine SAG mills 2. Flow chart 42, at step 44 the process starts, going to step 46 where the air gap monitoring system is used with a salient pole rotor to measure the minimum air gap 10 for each pole and for each air gap sensor. At step 48, the rotor 6 shape is extracted and evaluated at step 50 base on industry standards. If the rotor 6 shape is not acceptable, step 52 advices to stop the machine and proceed to the correction. Then the machine is restarted and gets back to step 44. Once the rotor 6 shape is acceptable as per step 50, the four anchors, right and left equipped with horizontal and vertical automated sole plates are going to get feedback as per the algorithms. Simultaneously step 54 and step 56 are starting there processing horizontal data step 54 and vertical data step 56.

[0042] At step 54, the average minimum air gap (AMAG) is extracted as a result of the twelve (12) air gap sensor outputs and the possible vertical positioning is extracted for the best horizontal positioning of the actuators 26, 28, 30, 32 on the right side (BHPR) and left side (BHPL). At Step 58, the actual position is compared to the best ones right and left. Difference between Actual Horizontal Position (AH Pi) and the Best Horizontal Position (BHPi) is Correction Horizontal (CHi). If the result is 0 within an error margin, the process proceeds with stop step 66 until a change of situation outside the set limits which brings the request for a correction. If the difference is outside of the accepted error margin, step 64 proceeds with the requested CHi on the actuator MHi. After correction is applied, resulting position is verified for a confirmation of the correction effect and if so step 66 stops the process until a change brings back the need for correction.

[0043] As for step 56 down, the same processing like step 54 is done for the vertical signals.

[0044] A second embodiment will now be discussed in relation with Figs. 6A, 6B and 6C. In this embodiment, it is assumed that the rotor has the proper shape, i.e. a rotor with poles having the same radius within their specifications. It will be noted here that such an embodiment can also be applied to a flat rotor machine.

[0045] Fig. 6A schematizes a machine 100 with salient poles equipped with four (4) actuators (Ai) 110, 112, 114, 116 (which can be sole plates in this case), four (4) proximity air gap sensors (VMi) 118, 120, 122, 124 and a feedback control system 126 which can have a computer connected as illustrated in Fig. 6B used to implement an algorithm such as shown in Fig. 6C, for instance. In the diagram of Fig. 6C, M is the number of actuators, S is the number of stator fixed sensors, i = 1 to M. This algorithm can be used for a flat pole rotating machine where M = S. From its four (4) air gap sensors 118, 120, 122, 124 and four (4) actuators 110, 112, 114, 116, S=4 and M=4, the sensors output are treated by the processor 128 using algorithms included in flow chart 130 Fig. 6C. The proper feedback information is sent to each actuator 110, 112, 114, 116 and the system can operate continuously in the form of a real time feedback control system 126 maintaining a suitable air gap 102 to the machine 100 all around.

[0046] As shown in Fig. 6C, an example control algorithm can be as follows: flow chart 130, at step 132, the process starts, at step 134 the air gap monitoring system measures the minimum air gap 102 for each air gap sensor 118, 120, 122, 124 and extracts the average minimum air gap of the whole machine (AMAG) from all the sensors 118, 120, 122, 124 around the stator 104. At step 136, the minimum air gap of local sensor (MAGi) is compared to the average minimum air gap of the whole machine to request the needed local correction: AMAG - MAGi = Ci. If“Ci” is 0 within a given error margin, the next step is 140 where the system is doing nothing until a correction becomes needed as per Ci value. If Ci is outside of the 0 margin value, the next step is 138 where Ci signal is sent to the local actuator Mi (i represents the actuator identification number since the number of air gap sensors can be higher than the number of actuators). The process is applied to each actuator positioned around the stator 104 where, at step 138, local actuator applies the requested correction Ci. After correction is applied, resulting position is verified at step 136 to confirm the targeted value and if the difference between them is zero (0) within certain error margin, the process ends at step 140 until a change in the situation shows a need for correction again using the real time dynamic feedback control system 126 algorithms. Whenever the difference of values at step 136 reaches a value outside the set limits, the process restarts at step 136 and so on. Error margins and hysteresis can be applied to avoid unstable system behavior. Moreover, a certain level of noise is to be expected, so hysteresis principles can be applied to avoid continuous back and forth movements. [0047] One way to obtain a measurement of the air gap 102 is by using a proximity sensor and by associating the amplitude of the proximity sensor signal to a corresponding local stator to rotor distance. Another way to obtain a measurement of the air gap 102, in the case of electric machines, is by monitoring magnetic field intensity, which typically increases when the air gap 102 decreases. Fig. 7 illustrates readings from both these types of sensors, with the proximity sensor reading 142 presented above, and the magnetic flux reading 144 presented below, and one can see how on a given machine, both readings can be strongly correlated.

[0048] A second embodiment will now be presented in relation with Figs. 8A, 8B and 8C. The algorithm of Fig. 8C is magnetic Flux based algorithm which can be used for a flat pole rotating machine.

[0049] As for the first embodiment, it is assumed a machine for witch the rotor has the proper shape. That second embodiment like the first embodiment can also be applied to a flat rotor machine. The same nomenclature is used for variables.

[0050] The second embodiment is referring to figure 8A and 8B an illustration of a machine 200 with salient poles equipped with four (4) automated sole plates, four flux probes 218, 220, 222, 224 and the feedback control system 226 for which the algorithms of Fig. 8C are applied. From its four (4) flux probes 218, 220, 222, 224 and four (4) actuators 210, 212, 214, 216, S=4 and M=4, the processor 228 gets signals 227 processes those signals 227 as indicated using algorithms included in flow chart 20. The proper feedback information 229 is sent to each actuator 210, 212, 214, 216 and the system operates in real time to produce a real time feedback control system keeping the right magnetic field and as such assumed to keep the right air gap 202 to the machine 200 all around. As indicated before, the air gap 202 and magnetic field can be directly correlated, and therefore, a magnetic field base system is applicable.

[0051] In Fig. 8C flow chart 230, at step 232, the process starts, at step 234, the flux probe signal is integrated to get the magnetic field intensity from each flux probe, the peak value of each probe is kept and the average peak value from all the flux probes is calculated (APMF) representing the average peak magnetic field for the entire machine 200. The peak value is the maximum amplitude positive or negative of the alternating current (ac) signal.

[0052] At step 236, the magnetic field peak value PMFi is compared to the average peak magnetic field value APMF to request the local correction: (APMF - PMFi = Ci). If Ci is 0 within a given error margin, the next step is 240 where the system is doing nothing until the correction become needed again. If Ci is outside of the zero (0) margin value, the next step is 238 where Ci signal is sent to the local actuator Mi (i is the actuator identification number and note that the number of flux sensors can be higher than the number of actuators). The process is applied to each actuator 210, 212, 214, 216 positioned around the stator 204. If Ci is outside of the zero (0) margin value, the next step is 238 where Ci is the correcting signal used by the local actuator Mi to proceed with the Ci displacement towards the wanted position. After correction is applied, resulting position is verified back at step 236 to confirm the targeted value and if the difference is within the error margins and hysteresis, the process ends at step 240 until a change in the situation shows a need for correction. That thanks to the real time dynamic feedback control system 226. So if the difference at step 236 becomes outside of set limits, the process restarts step 236. Error margins and hysteresis are applied to avoid unstable system behavior. Moreover, a certain level of noise is to be expected, so hysteresis principles can be applied to avoid continuous back and forth movements.

[0053] In the embodiments presented above, the stator 204 behavior dynamic shape correction can be performed in real time, while the rotor 206 shape can be fully taken care of at the time of assembly. The system can take care of the stator 204 good positioning around the rotor 206 for an optimum performance of the machine 200. The adjustments can be made to maintain the stator 204 shape in the optimal working condition taking into consideration the limitations due to its physical properties.

[0054] The process can take advantage of the air gap monitoring 225 results using them as feedback to keep a uniform air gap 202 and a well magnetic balanced electric machine. As such, it can constitute an air gap feedback system correcting the stator 204 at critical locations around the machine 200 in order to keep the average air gap uniform all around under its many working conditions. A smoother better-balanced running rotating machine can be achieved due to its constant magnetic pull through the uniform air gap all around. The adjustments can bring it as close as possible to the same air gap 202 value all around or at least within the standard specification.

[0055] The algorithms can be applied to flat rotor machines but since most cases are with salient poles rotor the described embodiments are referring to the salient pole. SAG mill is used as an example, but it will be understood that a similar system can be adapted to Ball mills, hydro generators, pumps storage and big motors, in other embodiments. The system can be configured to address other stator circularity defects than ovality.

[0056] Although the embodiments presented above use a plurality of actuators, it will be understood that in some situations, it can be preferred for the system to have a single actuator. For instance, if the rotary machine is fixed on one side, displacing the other side can be a satisfactory way of correcting ovality.

[0057] The system can be used, in various embodiments, to temporarily compensate for air gap variations caused by the non-concentricity of the rotor or by the mechanical wear of the rotor bearings, or to temporarily compensate for magnetic flux imbalance caused by rotor shorted turns, to name a few examples.

[0058] As can be understood, the examples described above and illustrated are intended to be exemplary only. The scope is indicated by the appended claims.